Variations in the transport, distribution, and budget of ²¹⁰Pb in sediment over the estuarine and inner shelf areas of the East China Sea due to Changjiang catchment changes

To investigate the impact of changes in the Changjiang catchment on the estuarine coast-shelf sedimentary system, variations in the transport, distribution, and budget of ²¹⁰Pb in the sediment of the Changjiang subaqueous delta (CSD) and the Zhejiang-Fujian coastal mud belt (ZFCMB) system were analyzed before and after the impounding of the Three Gorges Dam (TGD). The results indicate that the ²¹⁰Pb_ex activity in the surficial sediments of the CSD-ZFCMB decreased significantly after 2003 and that the surficial and vertical distribution of the ²¹⁰Pb_ex activity in the CSD changed substantially due to intensified sediment redistribution. The ²¹⁰Pb contribution of the Changjiang catchment to the CSD-ZFCMB is not negligible. Due to the trapping effect of the TGD, 76 ± 49% of the ²¹⁰Pb supply from the Changjiang upstream areas was retained in the TGD, resulting in the ²¹⁰Pb flux into the sea decreased substantially. Furthermore, our findings demonstrate that the cross-shelf plume provides a major conduit for the transport of ²¹⁰Pb over the East China Sea. The variation in the ²¹⁰Pb budget in the sediment of the CSD-ZFCMB also indicated that the influence of Changjiang catchment changes on the ²¹⁰Pb_ex and supported ²¹⁰Pb activities will become more significant in the future. In addition, the rate of ²¹⁰Pb burial in the sediments of the ZFCMB decreased, whereas the retention index of ²¹⁰Pb and the amount of ²¹⁰Pb retained in the CSD increased significantly, suggesting that after 2003, the material transfer function of the CSD weakened.